Conversion of hydrocarbons



'DSC- 11, 1956 E. w. s. NICHOLSON ETAL 2,773,811

CONVERSION OF HYDROCARBONS Filed Sept. 1S, 1953 EDWARD \N.S.NICHOI SON WVENTQRS FRANCIS R. RUSSELL ATTORNEY United States Patent O CONVERSION OF HYDROCARBONS Edward W. S. Nicholson, Baton Rouge, La., and Francis R. Russell, Mountainside, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware vApplication September 16, 1953, Serial No. 380,407

1 Claim. (Cl. 196-55) This invention relates to a process for treating hydrocarbons and more particularly relates to the cracking or coking of heavy residual oils -to produce lower boiling hydrocarbons and coke.

The hydrocarbon residual oil which is to be cracked according to the present process is a high boiling hydrocarbon oil which cannot be vaporized at ordinary pres sures without cracking the high boiling constituents. The residual oil may be that produced by distilling crude petroleum oil at ordinary atmospheric pressure or under subatmospheric pressure such as vacuum distillation. The present process may also be used for cracking or coking shale oils, pitches, tars, etc.

Processes are known in the prior art for cracking or coking residual oils in the presence of finely divided inert or substantially inert solids maintained as a uidized bed.

In the present process a dense iiuidized bed of finely divided inert refractory solids such as sand, coke, etc., is used and the preheated residual oil is introduced into the dense iluidized bed of finely divided solids maintained at reaction temperature. Vaporous products of coking are taken overhead and further treated as desired to recover lower boiling hydrocarbon fractions. During coking more coke is formed and some coke is withdrawn from the process. Coke particles from the coking zone or reactor are stripped to remove volatile hydrocarbons therefrom. Some of the stripped coke particles are withdrawn as product coke and the rest of the coke particles are passed to a burner where they are preferably .maintained in a dense uidized condition and contacted with air or other oxygen-containing gas to burn some of the coke particles and to supply heat to the coke particles. The heated coke particles are then returned to the coking zone to supply heat thereto. A transfer line burner may be used instead of a more conventional, low-velocity burner in which the particles are maintained in dense phase condition.

One of the problems in the uid coking of residual or other heavy oil feeds is the control of the particle size of the coke particles in the circulating coke stream. The most desirable particle size range for circulation in the system is that from about 75 to 400 microns. There is a gradual increase in size of the particles being circulated because coke is made from the oil feed and deposited on the Vparticles regardless of size. The coke made from the oil feed is deposited on the particles in a substantially uniform layer. As the circulating coke particles become coarser, uidization becomes poor, circulation more erratic and contacting efficiency decreases.

The above condition is aggravated by the combustion step in the burner because the smaller coke particles weight for weight have a relatively larger surface than the larger particles and will therefore be more easily burned by the oxygen-containing gas in the burner. It is desirable to remove coke particles coarser than the preferred size range as product coke and by the same token it would be most desirable if the bulk of the heat released 2,773,811 Patented Dec. 11, 195;Vl

ice

for the coking process by coke combustion were obtained from this undesirable coarse particle size range.

The very tine fraction of coke particles, produced by attrition, etc., cannot normally be held in the circulating system and is lost through the cyclone separators or other gas-solid separating devices. In operation of existing equipment, these lines are a complete loss because they are blown out of the top of the burner dense bed under conditions wherein little oxygen is present in the vent gas so that substantially no combustion and heat release or recovery from these fine particles is possible. t

Previous coking processes have required withdrawing coarse coke particles from the unit, grinding them and returning the ground particles to the unit. The present invention eliminates the necessity for such grinding of withdrawn coarse coke particles and return of the ground material to the unit.

According to the present invention the larger or coarse coke particles are preferentially burned in the combustion zone or burner by adding `a stationary packing material to the burner zone to cause the coarse coke particles to settle to the bottom of the burner zone where the oxygen or air or other oxygen-containing gas is tirst introduced. At the temperatures normally employed in the combustion zone or burner zone, the oxygen will be consumed and disappear rapidly; in other words, reaction rates will be quite high. Thus very little oxygen will reach the upper levels of the burner or combustion zone where the iine coke particles accumulate and substantially only the coarse particles will react with the oxygen. After the coarse particles have been burned sufficiently, their size is decreased by burning or spalling into smaller coke particles which are carried by the upowing gas into the upper portion of the burner zone and not consumed further. These smaller coke particles then act as seed coke and also improve iluidization and mobility of the circulating stream of coke particles.

In a more specific form of the invention, provision is made for burning fines normally 10st from the unit and recovering heat therefrom for the process. Coke particles from -the reactor or coking unit are mixed with a controlled amount of air ahead of or after a cyclone separator, and in the cyclone separator coarser solids are separated from fines which pass overhead. Combustion of the nes takes place in the overhead line. The hot iines are returned to the upper portion of the burner zone where they are mixed with and add heat to hot coke particles being returned to the coking zone.v The mixture leaving the burner is passed through a gas-solids separator device, the separated hot solids being returned to the coking unit while the burned nes are lost with the gas leaving the separator.

In the drawing the figure represents one form of apparatus adapted for carrying out the present invention but this showing is for purposes of illustration only and the invention is not to be restricted thereto.

Referring now to the drawing, the reference character 10 designates a reactor or coking zone containing a fluidized dense bed 12 of solid finely divided inert particles such as coke or the like. The dense bed 12 has a level indicated at 14 with a dilute or disperse phase 16 thereabove. The inert solids of the uidized bed 12 have a particle size between about 20 and 800 microns, preferably between about and 400 microns and may comprise petroleum coke, or other coke, coke formed in the process, spent cracking catalysts, pumice, Carborundum, alumina or other refractory materials.

The uidized bed 10 is maintained at a temperature between about 800 and 1600" F., preferably about 900'? to ll00 F.

When coking to produce motor fuel such as gasoline,

temperatures in the lower range of about 800 to about 1200 yF. will be used, whereas, when coking at extremely high temperatures -to produce chemicals such as,.unsaturatedhydrocarbon: gases .and .aromatic hydro.- carbons, temperatures-inthe higher lrange of aboutf1200? Frtoabout 160.05' F., preferably'about 1250*? tov 14509132, will.be,used.. Y Y

Thepreheated oil feed tobe converted-may be. .inf troduced :directlyfintothe dense -uidized highly turbulent bed-12,in the reactor or.I it may be introduced through feed .line .18V into riser 22 for distributingthe oil feed on the hotinert .solids comingfrom. the burneras will be later., described in greater detail. Steam and/or .feed may be introducedthrough .line .18-.` Ifsteam alone. is passedthroughline 18, the oil feed may be introduced further along ',.line 22 through line. 23. In some cases it mayhedesirable to y.feed or Vspray the oil feed into Ithe Y dilute phase 16above the dense bed level 14. The oil feedis .preferably preheated-.in any suitable manner .to a temperature between about 600 and.800. F. before being introduced into the reactor 10. The oil feed comprises.aresidualpetroleum oil such as tar, pitch, crude residuum, heavy bottomsfor other similar hydrocarbon stock having an API gravity between about -10 and 20, a'Conradson carbon betweenvabout 5 and 50 wt. percent and aninitial'boiling point between about 850 and 1200 F. Steam may be introduced at one or more points 24 toassistin maintaining the. bed inuidized condition.

The fluidized bed 12 is maintained as such by the upilowing hydrocarbon gases and vapors formed by the coking of the oil ffeedand by the. steam added=to the process. The superficial velocity ofthe gases and vapors passing upwardly through the bed 12 is between about 0.5 and,4 feet per'second when using finely divided coke of about 50 to 400 microns and at a superficial velocity of yabout l to 2 feet per second, Ythe density of the uidized bed .will be about 40 lbs. per cu. ft. but may vary between about.l5 and 60 lbs. per cu. ft.. depending on the gas velocity selected andthe particular. particle size range.

Vaporous products of coking leave the .bed 12 and pass overhead into inlet 26 of cyclone separator 28 arranged .at-the top interior of the reactor 10. The vaporous yreaction products leaving ythe coking zone vcontain .entrained solids and thev cyclone separator '28 or other gas-solids .separating device is used .to separate or recover the entrained solids and return them to the densefluidized bed through dipleg 32.. More than one cyclone separatorin stages maybe usedand the cyclone separator or separators'may be arranged externally of thereactor .10. n

The. separated reaction vapors pass overhead from the cycloneV separator 2S'through 1ine34 and are further treated in any suitablemanner to recover gas, gasoline, gas oil, etc.

Coke .particles .are withdrawn downwardly. from the dense.bed12.into. stripping zonevor vessel'36 which is shown as having -a smaller. diameter .than reactor.10 and which extends downfromreactor, as an integral structure.. .Other forms of stripper imay be used.. Steam or other strippingl `gas is introduced through lineor lines 33.intov the :bottomzportion of the stripping zone36 to remove volatile hydrocarbons'from the coke inthe stripping zone andV passthemtupwardly 'into the dense fluidizedbed 12in reactor'10. The. temperature inthe stripping yzone is between about800 and .1600"v F. and the velocityY of Vthel upowing gas in the strippenmay be between about.().4Y and 2.0 feet per second tomaintain. a denseiluidized mixture.

Stripped coke particles are removedfrom .thebottom of ,thestripper. through line. 42 .to which uidizing Agas may be addedthrough one 4or more lines.44.f. Line42 is formed as a U-bend 46 and the solids ltherein are 4 1l, 1952, and a further description is not necessary here. Gas such as steam or the like in a small amount is add'ed at the bottom of the U-bend 46 as at 48 to maintain iluidity of the solid particles.

According to one method of operation according to the present invention vand in orderto reduce or remove the coarse coke particles in the circulating stream which are formed by successive layers or depositsof coke on the particles .during the coking process, thefcokeparticles in U-bend 46 are'passed through riser 52 into the-lower portion of a packed elutriator-burner 54, As yabove' pointed out the coke particles increase in size-because of the formation and deposition of more coke on the coke' particlesr in the circulating stream'vand'zi these coarse particles having a particle size bigger than about 500 to 1000 microns must be removed or somehow reduced in size if they are to remain in the unit. According to the presentinvention the coarse particlesare selectively: burned to remove themor to make smaller.. particles within the desired range of 75 4vto v400 microns.; i

.The upow leg 52'of U-bend 46 Vis provided .witl'a .variable restriction such-as a .slide valve 56V to. assistfin' the control of circulation of solids. Steam or thelike is introduced into rser'52` through'lin'e v58-"abtve' restriction 56 to. control the rate of iowv of solids to burner 54. Upow leg 52v empties into. the lower-portion of the burner 54 but. preferably above the .bottom thereof. If desired, leg. 52 may empty into burner 54 at ahigher level than shown in the drawing. l Y

Air or other oxygen-containing .gas isV introduced through line 62 into the bottom portion. of burnenf54 below thev locus of introduction offthe `coke particles passing through line 52 to preferentially burnthefcoar'se coke particles collected in the bottom of' bi11 ner-.-54-bI elutriatiorn At the temperaturesnormally employed in the burner54, the oxygen in the gas introducedfthi'o'ugh line 62 will be consumed and disappear, rapidly .and very little oxygen-containinggas will reach .the upper levels of the burner 54 where the line. particles accumulate. Most of-the oxygen will be consumed inthefst few feet of travelthrough the cokefbed inthe burner in cases where the temperature islbetween about 1000. and 'l700 F.

The elutriating burner 54 is'packed with 'a non-idizable material-such as Berl saddles, Raschig `rings,.bals of various. shapes, spaced chainshangingdown .through the bed, etc., the packing being rdiagrammaticallyvr shown by cross hatching v64.l For a burner having. a .diameter of about y5 to2() feet, Berl saddlesof about .1v/2i to.4fin`ches may be used. .The superficial `velocity of theaupowing gas in burner 54 is between .about 2.0 and .6.0ft."/sec. and. is suicient to .carry overheadthroughline 661the middle-sized and liner particles. The. particle size ofthe solids going overhead is about 504 to 400 microns.

The gaseous suspension passing overhead through line 66 isintroduced Yinto gas-solidsfseparating.;means 68-such as one or more stages ofv cyclone .separators. The. separated combustion .gases pass overhead .through line 72 and the separated -solids are passed to standpipe 74 which mayhave one or more -uidizingor aerating lines 76. Standpipe 74 formsone leg. of anotheLU-bend 78 having a bottom aeration :line 82 -throughf which .gas such as steam is introduced inamount.suflicientronly-,to maintain thesolids in a fluidized condition lin theVU-bend .78. The riser 22- (previously referred-to) of:U-bend78 has a valve 84 orvother variable restriction or-ice vto assist in controlling. the `ow ofthe circulating-so1ds. The function of` restriction 84 is .the sameas lthatlabove described.forrestriction` 56.l 4

Some. of the hot-coarse solids mayefbe withdrawn from .theA bottom portiorrofburnerY 54 throughf line and .introduced into U-bend 78 `for-.recycler'ta,oking bed..12, .if desired.. Some oftherhotfcoarse so1ids.may be withdrawn fromline 86' through..line88 .as :product coke after proper cooling or quenching. v

In a more specic form of the invention, provision is made for preferentially burning fines and recovering heat from these particles which are usually lost from the system. In addition provision is'made for burning the coarse coke particles in elutriating burner 54 as above described in connection with the broader form of the invention. In this specilic form solids from U-bend 46 are passed through riser 92 provided with a valve or other restriction orifice 94 rather than through line 52. Steam or other gas is introduced into riser 92 above valve 94 through line 95 and the amount of steam introduced controls the rate of ow of solids through riser 92. Ahead of cyclone separator 96 or other separating means, a gas stream containing a controlled amount of oxygen may be introduced through line 98 into riser 92. In separator 96 the bulk of the solids is removed and the fines and gas pass overhead through line 102. Burning of the nes or ne fraction of the circulating stream is started and continues in the overhead line 102 containing the iines and the oxygen-containing stream.

The quantity of oxygen introduced into this tine particle system is so regulated that there will be essentially no oxygen remaining at the outlet of line 102 where it opens into the upper portion of the burner 54. Overhead line 102 is elongated to permit time for burning a substantial fraction of the lines stream and particularly the smaller particles in this stream. Line 102 is shown as an inverted U-bend but may take other forms.

Instead of introducing the oxygen-containing gas through line 98, gas containing no oxygen may be introduced through line 98, or introduction of gas at this point may be eliminated entirely, and air or other oxygencontaining gas in controlled amount added to line 102 through line 104, if it is desired to eliminate any possibility of burning coarser particles in this part of the system.

The coarse fractions of the circulated solids separated out in the cyclone separator 96 and containing particles larger than about 50 to 100 microns, are passed down through standpipe 106 which may be provided with one or more uidizing or aerating lines 108. Standpipe 106 forms part of U-bends 109 and 110 which are similar in construction and operation to the U-bends previously described.

Upper U-bend 109 has bottom fluidizing line 112, variable restriction 114 in riser 11S and a line 116 for introducing a gas above restriction 114 for controlling ow of solids through riser 115. The gas introduced through line 116 is preferably a gas such as steam. Riser 115 opens into an intermediate portion of burner 54 above the outlet of riser 52 of U-bend 46 above described. As above described, oxygen-containing gas such as air is introduced through line 62 into the bottom of elutriating burner 54.

Lower U-bend 110 has aerating bottom line 118, riser 120, variable restriction 122 and gas introduction line 124 above restriction 122. Gas such as steam is introduced into riser 120 through line 124 for control purposes. Gas in line 124 may contain oxygen.

The U-bends 109 and 110 may both be used so that solids from standpipe 106 pass both into the bottom portion and intermediate portion of burner 5'4 or only one U-bend may be used for introducing such solids either into the bottom portion of burner 54 or into an intermediate portion of burner S4.

In the elutriating burner 54 a controlled quantity of air is introduced through line 62 and the superficial velocity of the gases owing up through burner 54 is selected to be between about 2.0 and 6.0 feet/sec. so that middle-sized coke particles of about 75 to 400 microns are elutriated overhead without substantial combustion of these particles. The coarsest particles (approximately 400 to 1000 microns) fall to the bottom of the burner 54 and are retained there, and consume by combustion essentially all the oxygen which is introduced into the bottom of the burner 54 through line 62. During burning of the coarse particles in the bottom of burner 5'4, the coarse particles are reduced in size and become fine enough to be moved up in the elutriating burner forrecycle to the coking zone. During burning some of the coarse coke may spall orothen wise break down into smaller pieces.

The middle sized particles are elutriated overhead from the burner without substantial loss due to combustion. The elutriated particles pass through line 66 above described and then through cyclone separator 68 for recovery of hot solids which are -returned to coking zone 12 through U-bend 78. The hot gas and tine coke or ash particles leaving the lines burner line 102 are combined with the elutriated middle size particles from elutriating burner 54 at the top of the burner 54 or by being introduced into line 66 leading to nal cyclone separator 68 so that the heat available in the gas-tines stream is recovered by the middle size particles recovered in cyclone separator 68 for circulation back to the coking zone 12. The burned fines are lost to the atmosphere through line 72 leading overhead from cyclone separator 68. The middle size particles leaving the top of the burner 54 are essentially unburned but they are heated by Contact with hot particles and by the hot combustion gases passing up through the burner 54. The hot combustion gases are formed by burning the coarse colte particles at the bottom of burner 54.

In this form of the invention a circulating solids stream of an optimum particle size is maintained while obtaining all the heat necessary for the coking operation by selectively or preferentially burning the undesirable ne and coarse fractions of the coke. Some hot coarse particles may be withdrawn through line 86 from the bottom of burner 54 and introduced into line 74 containing middle sized particles for supplying additional heat to the particles being returned to coking zone 12.

During combustion of the coarse coke particles in the burner 54 the temperature is between about l000 and 1700 F. Additional heat is added to the medium sized particles from the fmes burned in line 102 so that the particles being recycled to coking bed 12 through U bend 78 are at a temperature between about ll00 and 17 50 F. and contain suicient heat to vaporize and crack or coke the feed oil introduced into coking zone 12.

In cases where more heat is required than is being produced by burning coke in burner vessel 54, oil or gas or other fuel may be introduced into vessel 54 through line 128 or hot combustion gases may be supplied to burner 54.

In a specic example about barrels per day of residual oil having an API gravity of 10 and a Conradson carbon of 18 and an initial boiling point of about 1150 F. and about 7000 lbs. per day of steam are added to the the dense bed 12 in reactor 10. The oil feed is preheated to about 600 F. The solids to feed oil ratio by Weight to the reactor is about 15 to l. 'Ihe temperature in the reactor is about 1000 F. and in the burner is about 1l50 F. About 2 to 3 gallons per hour of oil are injected into the burner 54 through line 128 to provide for heat losses in this small pilot plant.

The circulating solid is coke formed in the process having a particle size of about 50 to 800 microns with the majority of the particles being between about and 300 microns. The superficial velocity of the gas in the reactor 10 is about 1 ft./sec. at the bottom of the cylindrical portion and the density of the dense uidized bed 12 is about 45 1bs./ cu. ft. The superficial velocity of the gas in the burner 54 is about 3 ft./sec. and the density of the dense uidized bed 55 is about 40 lbs./cu. ft.

The stripper 36 is at a temperature of about995 F. and

artsen..

thersupercial velocity ofthe stripping. steam passing; upf.

wardly throughI vthe .stripper is about. 1.0 Vft./ sec.

The:l overhead productsl leavingcyclone separator12'8- through vline 34 lare at a temperature of aboutV 1000 F.- andare quenched to a temperature of aboutY 800 F.

' The yields obtained are as follows:

About 65V lbs. of coke per hour are withdrawn as product coke through line 88.

Coke particles from line.52 are introduced into the lower portion of burner 54 butfabove the bottomthereof to'eiect elutriationof the coke particles in the burner 54 packed with Berl saddles. Air is introduced into the bottom of the burner through line 62. The coke particles n going to elutriating burner 54 throughline 52 have .a particle size between about 50 and 800microns with about 30 to 50% by weight of iiner particles. having a particle sizey between 50-and.200 microns andabout 5 to by wt. of coarse particles having a size between about-300 and 800 microns.

In the elutriator burner. the. ner particles of the de?. sired size between about 50 and 400 microns ,pass upupwardly through burner S4 and the coarse particles larger than about 400 microns fall to the bottom vof the burner 54 wherethey are preferentially burned with air introducedl through. line 62. Most of. the oxygen is quickly consumedina few feet oftravel (about.4 feet) in. .burner 54 so that substantially none of the liner particles of the desired particle .size are burned but they are heated by the combustion gases flowing up through thel burner formed by burning the coarse coke particles in the bottom of the burner 54. For about 70' lbspof coke burned off the coarse particles per hour about 750 to 900 lbs.of air per hour are'used and there is substantially no oxygen .in the' overhead stream in line 66. Duringvburning, the coarse particles are reduced'in size and whenthey `become small'enough they are entrained with the upowing gas throughline 66' and returned to the cokingl zone. 12 through U-bend 78. .Also duringlburnin'g of the. coarse coke particles, spalling or breaking up of the particles Vto-smaller.particles may occur.

With the present invention it is possible in most cases to main/tain the proper size of coke particles inV the circulating Vcoke stream without the necessity of withdrawing coarse coke particles, grindingth'em and then returning the 'ground particles to' the circulating coke stream.

instead of passing the coke particles from U-bend'46 to burner 54 directly, 'they Amay be passed'through riser 92 'to cyclone separator'96to separate lines having'a particle size Aabout 75 micronsor less." Thenes are mixed'withairV th'roughflinev 104 to'fburn them'and re-v coverfheat therefrom; Forrabout SOlbs. to 800 lbs.

perz-hour of nespassing through line 102, a limited.A quantity. of air, thatis,'aboutr100.to-400lbs. of air per:

hour.isintroducedthrough line .104'. The nes stream g atatcmperatureof about 1100" to 1800"A F. and withVv no freeoxygen is passed to` ther-top ,of burner 54l to supply. heat toxthe middle sized particlesl leaving the..

elutriator burner 54 overhead. l Thezcoarser coke yfraction having a particle size large. lybetween 75 and 800 microns iswithdrawn from cyclone separator means 96 and passed through U-bend 109 to an. intermediate portion of elutriator burner 54 wherein the; coarse particles. settle to the bottom and are burnedas.

abovedescribed and the middle sized particles or particles.

having;the. desired particle size-range go overhead fromf burner 54.- The burned nes and middle sized particles; pass.l overhead .through line `66to separatorv 68 where. fines are lost overhead and the desired size particles are:`

recycled to the coking zone 12.v

Instead of passing allY the coarse solids from standpipe 106 throughl U-bend 10,9, all or part of the coarse solids,

from standpipe 106 may be passed througlrU-bendfllt) into the bottom portion .of burnerv 54.v Whatis lclairned is:

A method.V of .coking a heavy residual hydrocarbon which comprises ythe steps of contacting a heavy residuall hydrocarbonoilwith a dense bed-of uidized coke para ticulate solids inV a. coking zone maintained atcoking temperature by hot coke solids-recycled from a burningV zone to the coking zone, the coking reaction being ,accompaniedbythe deposition offcoke on the solids and increase in size..thereon; removing vaporous reaction productsoverhead from the..coking zone; removing'cokeV solids from the .coking zone; passing an oxygen-centaine;

- ing gas throughgthe coke solidsand .selectively removing therefrom cokeneshaving a diameter of less than about 75microns; .burningthese coke fines in the form ofa confined stream in the oxygen-containing gas; passing theV Y to 400 microndiameter particles entrained .in gaseous productsof combustionV overhead from lsaid burning zone; co-mingling the products ofcombustion from the coke-nesfburning step therewithj separating combustion Y References Cited in the tile of this patent UNITED STATES rPATENTS 2,661,324 Leier Dec.- 1,1953 

